Shuumatsu Nani Shitemasuka Isogashii Desuka Sukutte Moratte Ii Desuka

Summary:
Five hundred years have passed since the humans went extinct at the hands of the fearsome and mysterious 'Beasts.' The surviving races now make their homes up on floating islands in the sky, out of reach of all but the most mobile of Beasts.

Only a small group of young girls, the Leprechauns, can wield the ancient weapons needed to fend off invasions from these creatures